Fluid actuators



p 1963 J. R. CLIFTON ETAL FLUID ACTUATORS 4 Sheets-Sheet 1 Filed Dec. 28, 1960 p 19.63 J. R. CLIFTON ETAL FLUID ACTUATORS 4 Sheets-Sheet 2 Filed Dec. 28, 1960 INVENTORS 4 John R. Clifton Carl H. Johnson P 24, 1963 J. R. CLlFTON ETAL 3,104,593

FLUID ACTUATORS 4 Sheets-Sheet 3 Filed Dec. 28, 1960 Sept. 24, 1963 J. R. CLIFTON ETAL Filed Dec. 28, 1960 FLUID ACTUATORS 4 Sheets-Sheet 4 /00 "L, I I /02 INVENTORS John, R. Clifton Carl ILJohnson Frank S-Pea ne aytfi MW ATTORNEYS United States Patent 3,104,593 FLUID ACTUATORS John R. Clifton, Rolling Hills, Carl E. .l'ohnson, Bnena Park, and Frank S. Peame, Alhambra, Calih, assignors to Regent Jack Mfg. Co., Inc, Downey, Caiiil, a corporation of California Filed Dec. 28, 1969, Ser. No. 79,027 19 Claims. (Cl. 9217) The present invention relates generally to fluid actuators, and more specifically to a new and improved pistoncylinder type fluid actuator for supporting heavy objects or maintaining controlled separation of relatively movable members.

The invention is particularly concerned with applications of piston-cylinder type fluid actuators, jacks, and the like Where it is desirable to maintain the piston ram in a predetermined extended position within the limits of its stroke under variable loading conditions which may tend to either increase or decrease the fluid pressure in the cylinder. The invention is also concerned with maintaining the piston ramin such an extended position in the event of any uncontrollable failure of pressure or change in pressure in the fluid line to the fluid actuator, while permitting intentional movement of the piston ram when desired.

The effects of abruptly changing the loading conditions under which the fluid actuator is operated will be made apparent by assuming a basic application in which a con ventional actuator is used to support the free end of a second class lever so that the ram is under compression loading. If the weight is suddenly shifted beyond the fulcrum to create a first class lever, the normal compression load on the ram will be changed to a tension load,

and the ram may be rapidly and uncontrollably extended to the limits of its stroke. This same undesirable ram movement also would obviously occur in the opposite direction if the normal tension load of a first class lever were changed to create a second class lever. In the latter instance the load on the ram would be subjected to a reversal from tension to compression and might be forced to retract within the cylinder. The hazards of ram movement due to hydraulic pressure failure or uncontrolle change in hydraulic pressure are obvious.

It is recognized that many conventional hydraulic lifting jacks have been provided with a wide variety of mechanisms for locking the ram against retraction should there be an abrupt increase in the compression loading on the jack ram and/ or failure of fluid pressure. However, there has been no effective and dependable construction for maintaining the ram in a fixed position Within the limits of its stroke by preventing both accidental retraction and accidental extension of the ram.

Accordingly, an object of the present invention is to provide a piston-cylinder type fluid actuator wherein movement of the piston ram may be prevented independently of the exerted load and/ or accidental fluid pressure changes in the system.

A more specific object of the invention is to provide a novel ram-locking mechanism :for a fluid actuator of the type described which is effective to lock the ram in a selected position of extension even though the exerted load may reverse direction.

A further object of the invention is to provide a ramlocking mechanism as described in the previous paragraph which is further characterized by a sturdy construction and a reliable, relatively simple operation.

In general, the invention contemplates a fluid actuator embodying a pressure-responsive locking mechanism for controlling movement of the ram by or in opposition to the loads to which the actuator is subjected. Preferably, this locking mechanism is in normal locking engagement Ice with the ram and is disengaged to permit movement of the ram in response to fluid pressure created in the cylinder for that purpose. As will hereinafter become more apparent, when such an arrangement is provided in a hydraulic lifting jack, the jack ram. will be locked against extension until a predetermined cylinder pressure is created and maintained. If the exerted load is changed from a compression to a tension load when the ram is in a partially extended position, thereby affecting a decrease of fl-uid pressure in the cylinder, the pressure responsive looking mechanism will re-eng-age the ram to prevent extension.

Advantageously, the fluid actuator also may be provided with a second manually releasable locking mechanism for preventing reverse movement of the ram in the event of either fluid pressure failure or a sudden increase in the normal applied load which exceeds the fluid pressure in the cylinder.

It will thus be apparent that the invention provides a fail-safe construction for maintaining the ram of a fluid actuator in a desired fixed position under variable loading and pressure conditions, and that the position in which the ram is locked may be precisely controlled by simply adjusting the pressure required to disengage the pressureresponsive locking mechanism.

Many practical applications of the invention, together with additional objects and advantages, will become apparent from a consideration of the following detailed description and the accompanying drawings.

In the drawings:

FIGURE 1 is a vertical cross-sectional view of one preferred embodiment of the invention.

FIGURE 2 is a cross-sectional view taken on the line 22 of FIG. 1.

FIGURE 3 is a cross-sectional view taken on the line 33 of FIG. 2 and shows the actuator ram locked against movement in either direction.

FIGURE 4 is a fragmentary cross-sectional view in the plane of FIG. 2 but showing the actuator ram unlocked for movement in one direction.

FIGURE 5 is .a fragmentary cross-sectional view in the plane of FIG. 3 showing the actuator ram unlocked for movement in the opposite direction.

. FIGURE 6 is a vertical cross-sectional view of another embodiment of the invention.

FIGURE 7 is a cross-sectional view taken on the line 7-7 of FIG. 6.

FIGURE 8 is a schematic illustration of a typical use of fluid actuators constructed according to the invention, in which the actuators are operatively connected to raise a load-bearing platform.

Referring first to FIG. 8, there is illustrated a typical environment in which one or more fluid actuators constructed in accordance with the present invention may be advantageously used. Four such fluid actuators, only two of which are shown and designated by reference numeral 10, are provided for raising the platform 11 against a load W to an elevated, horizontal position above the base 12 and for holding the platform in that position even though the load W may be moved from one end of the platform to the other. This movement of the platform is accomplished by expansion of the toggle joints l3 and 14, which are comprised ofthe links 13a and 13b and 14a and 14b, respectively. The links 13a and 14a are pivotally connected to depending portions of the platform 11 near opposite ends thereof and the links 13b and 14b are pivotally connected to the base. A fluid actuator 10 is operatively disposed between the links of each toggle joint so that the toggle links will be separated or expanded when the rams of the actuators are extended to thereby lift the platform.

It will be observed that the rams of the actuators 10 will be normally subjected to compression loading. However, if the weight W is moved from the center (solid arrow) to the end (dotted arrow) of the platform beyond the pivotal connections of the links 14a as illustrated in FIG. 8, the loading of the actuators at the opposite end of the platform will be changed to one of tension, while the compression loading on the actuators connected to the links 14a will be increased. This change in the load ing conditions obviously produces a tendency for the platform to tilt.

In accordance with the stated objects of the present invention, the fluid actuators are constructed to include a novel ram locking mechanism for holding the actuator rams in selected positions of axial extension. When embodied in the structure illustrated in FIG. 8, the ram locking mechanism of the invention is effective to maintain the platform 11 in a fixed horizontal position even though the loading on the rams platform may be thereafter varied in the manner described as the weight W is moved.

In FIG. 1, the basic construction of the fluid actuators 10 is shown to be more or less conventional and to comprise a cylinder 15 which is closed at its bottom end by a plate 16 and partially closed at its upper end by a plate 17. A ram 18 extends upwardly through the plate 17 from a connected piston 19 reciprocal in the bore of the cylinder, the piston 19 being formed with a peripheral groove in which is disposed a sealing ring 20. The upper end of the ram 18 and the lower end plate 16 are provided with axially extending ears 2]. which may be fastened within upper and lower clevises 22. These clevises 22 may be in turn secured to the relatively movable members, such as the toggle arms 13a and 13b and 14a and 14b of FIG. 8, which are intended to be forced apart by operation of the actuator.

In the illustrated construction, the actuator 10 is intended to operate under normal conditions of compression loading such as described in connection with FIG. 8. To this end, the lower cylinder plate 16 is provided with a passage 27 which is in communication with a conduit 28 threaded into the side of the cylinder 15. This conduit or pipe 28 may be connected to either a hand pump system (not shown) for introducing fluid into the cylinder below the piston 19 or directly to a suitable pressurized fluid source (also not shown). In either case, it will be evident that the illustrated construction provides for a one-way operation in which a build-up of fluid pressure between the lower cylinder plate 16 and the piston 19 will be eflective to extend the ram while the loading on the ram will cause it to retract when the fluid pressure is relieved.

In accordance with the principal objects of the invention of providing a mechanism for locking the ram in a selected extended position, the ram 18 is formed with a helical groove 32 which extends substantially the full length of the ram. In the preferred embodiment of the locking mechanism, the helical groove 32 is lockingly engaged by an interfitting inner tooth 33 of a nut 34 which is positioned at the top of the cylinder 15, as shown most clearly in FIG. 3, the nut 34 is mounted between the upper cylinder plate 17 and an axially spaced thrust bearing plate 35 fixed within the bore of the cylinder. For purposes which will become more apparent, a pair of thrust washers 36 preferably are provided and these thrust washers are pressed into contact with the upper and lower surfaces of the nut 34 by spring washers 37 which are seated in recesses 38 and 39 formed in the plates 17 and 35, respectively. A small amount of clearance is provided between the nut 34 and the plates 17 and 35 so that the spring washers 37, which are axially bowed toward each other, function to normally suspend the nut out of contact with the outer annular shoulders that are defined by the recesses 38 and 39 in the plates 17 and 35.

Inasmuch as the cylinder 15 and the ram 18 are prevented from rotating with respect to each other by attachment of the ears 21 within the clevises 22, it will be 4 seen that either extension or retraction of the ram will cause the nut 34 to rotate. The suspension of the nut between the spring washers 37 advantageously minimizes the frictional force tending to oppose such rotation. Converse-1y, if the nut is held against rotation, the ram 18 will be effectively locked to prevent axial movement thereof except to the extent permitted by collapsing of one or the other of the springs 35.

The outer circumferential surface of the nut 34 is shaped to provide spaced, radially extending teeth 42 having tooth spaces 43 therebetween. These tooth spaces 43 may be selectively engaged by a sloping tooth 44 of a one-Way pawl 45 for preventing clockwise rotation of e the nut 34, as viewed in FIG. 2, and hence extension of the ram. Referring particularly to FIGS. 2, 3 and 4, it will be seen that the pawl 45 is a piston of a T-shaped configuration as viewed in cross-section and is mounted in a correspondingly configured bore 46 of a cylinder block 47. The cylinder block 47 is mounted in the upper side of the cylinder 15 radially outwardly of the nut 34 with the small end of the bore 46 opening into the cylinder so that the pawl tooth 44 may be engaged in the tooth spaces 43 by movement of the piston-pawl 45 inwardly to the inner limit of its stroke FIG. 2).

The pawl tooth 44 is normally held in engagement with the tooth spaces 43 of the nut 34 by a compression spring 50 which acts between the head 51 of the pawl 45 and a retention plate 48 secured to the outer end of the cylinder block 47 by screws 49. Reverse or disengaging movement of the pawl against the bias of the spring 50 is atfected hydraulically by introducing fluid into the cylinder block bore 46 behind the pawl head 51 to force the pawl to the position shown in FIG. 4. 'For this purpose, a fluid conduit 52 is connected to the cylinder block 47 and this conduit communicates with the large end of the bore 46 by way of a fluid passage 53. Preferably, both the large and small ends of the pawl are formed with peripheral grooves for receiving sealing rings 54 and 55, respectively, which prevent fluid from leaking into the cylinder 15 and into the cylinder block bore at the front of the pawl head 51. The cylinder block 47 also may be provided with a pin 56 which extends freely through a slot '57 in the stem of the pawl and in each direction with a close fit into the cylinder block 47 for limiting movement of the pawl in either direction.

In the preferred embodiment of the invention, the conduit 52 is in fluid communication with the cylinder 15 below the piston 19, the lower end of the conduit connecting through the cylinder wall to a passage 58 in the lower end plate 16. This construction is such thata portion of the fluid pumped into the cylinder 15 to raise the ram 18 will be diverted through the conduit 52 to actuate the pawl 45, thereby disengaging the awl tooth 44 from the nut 34 so that the latter is free to rotate in a clockwise direction. The biasing force exerted by the spring 50 and the relative areas of the piston 19 and the pawl head 51 are selected to be such that the pawl 45 i will be actuated by a pressure less than that necessary to overcome the frictional force opposing movement of the ram 18 in an unloaded condition.

Under some circumstances it may be desired to manually release the pawl 45 without relying on fluid .pres- I sure, as, for example, when the fluid actuator is being 47. A ring 60 or other suitable handle may be secured to the head of the bolt 59 so that the pawl may be manually pulled outwardly against the bias of the spring 50. i

A second one-way pawl 66 having a sloping pawl tooth 67 is provided for locking the nut 34 against counter clockwise rotation, as viewed in FIG. 2. This pawl 66 is shown as being in the form of a cup-shaped plunger which is mounted for reciprocation in a housing 68. The housing 68 is diametrically opposed to the cylinder block 47 and is mounted in the wall of the cylinder 15 so that the pawl 66 may be moved toward the nut 34 to engage the pawl tooth 67 in the tooth spaces 43. The pawl 66 is pressed into normal engagement with the nut 34 by a compression spring 69 which is carried in the housing 68 between the bottom of the cup-shaped pawl and the outer end wall of the housing. When in engagement with the nut, the pawl 66 serves as a safety device for preventing retraction of the ram under severe compression loads or when there is a fluid pressure failure in the cylinder 15.

A bolt 70 passes with a free sliding fit through an opening in the outer end wall of the housing 68, and this bolt has its inner end threaded into the bottom of the cup-shaped pawl 66. The outer end of the bolt 70 carried a washer 71 which abuts the end wall of the housing when the pawl is in its normal locking position. In order to retract the pawl 66 to the position shown in FIG. 5, there is provided a cam arm 72 which is pivotally connected to the end wall of the housing 68. As shown, this cam arm '72 is substantially L-shaped and is connected to the housing 68 in a slot 73 which is formed in the housing end wall beneath the washer 71. The small leg of the cam arm is pivoted on a pin 74 extending into th opposite side walls of the slot 73, between the washer and the bottom of the recess 73, so that, when the cam arm is rotated, the washer will be forced away from the housing end wall to pull the pawl 66 out of engagement with the nut 34. To permit this disengaging movement of the pawl 66, it may be necessary to slightly raise the ram 18 hydraulically to relieve the load exerted by the nut 34 on the pawl.

In operation fluid under pressure is admitted through the conduit 28 to the cylinder 15 below the ram piston 19, it being assumed that the ram is under compression loading. A portion of this fluid is diverted through the conduit 52 to the cylinder block 47 to force the pawl 45 out of engagement with the nut 34 from the position shown in FIG. 2 to the position shown in FIG. 4. As explained above, this disengagement of the pawl 45 occurs before any movement of the ram which might damage the pawl tooth 44. Thereafter the fluid under pressure may be supplied to the cylinder 15 until the ram :18 has moved to the desired position, at which time the fluid supply is cut-off. As the ram extends, it will be apparent that the coaction of the nut teeth 33 in the helical groove 32 will cause the nut 34 to rotate clockwise (FIG. 2) in ratcheting engagement with the pawl 66.

When the ram 18 has been forced to the selected position of extension, any tendency of the ram to retract from that position is opposed by locking engagement of the pawl 66 with the nut 34- to prevent it from rotating counterclockwise (FIG. 2), which eifectively locks the ram against retraction into the cylinder 15. Conversely, any tendency of the ram to continue to extend beyond the selected position would necessarily effect a pressure decrease in the cylinder 15 and result in the pawl 4-5 being forced by the spring 50 into locking engagement with the nut 3 This locks the nut against clockwise rotation (FIG. 2) and, hence, locks the ram against continued extension. Thus, it will be seen that the invention provides a locking mechanism for selectively holding the ram in a desired position and preventing ram movement regardless of changes in the applied load. At the same time, the ring 6% and cam lever 72 permit selective manual release of the ram to extend freely under a tension load, to retract freely under a compression load, or both, as may be desired under various circumstances in use.

The locking action described above and the general operation of the fluid actuator is enhanced by the preferred construction in which the nut 34 is between the thrust washers :36 and the spring washers 37. The spring washers are sufficiently strong to resist collapsing under the axial component of the frictional force created between the nut teeth 33 and the helical ram groove 32 and, as previously explained, these spring washers space the not between the plates 17 and 35 for relatively free rotation. However, it will be apparent from FIG. 3, that if the load on the ram 18 changes from compression to tension and causes the pawl 45 to engage the nut, the upper washer 37 will collapse into the recess 38 so that the nut 34 bears against the plate 17. In this manner, the force tending to cause axial extension of the ram will advantageously be transmitted to the shoulder of the plate 17 around the recess 38, while the torque load on the pawl 45 will be partially relieved by the additional frictional force developed between the nut and the plate.

Similarly, if there is an abnormal compressive load or a failure of fluid pressure, the lower washer 37 will collapse in the recess 39. This permits the nut 34 to move against the plate 35 so that the axial load will be transmitted to the plate and an additional frictional force will be created to partially relieve the torque load on the pawl 66.

Reference is now made to FIGS. 6 and 7 which illustrates a modified construction of the locking mechanism comprising the present invention. The basic construction of the fluid actuator is again more or less conventional and includes a cylinder shell 86 which is closed at its ends by upper and lower cylinder heads 81 and 82., respectively. Reference numeral 83 designates the ram, which is connected at its lower end to the piston 84 and extends upwardly through the upper cylinder head 81. As in the case of the construction shown in FIGS. 1-5, fluid under pressure from a suitable source (not shown) is admitted to the cylinder below the piston through a conduit =85- and a passage 86 formed in the lower cylinder head 62. The upper end of the ram and lower head 82 are provided with ears 87 which may be respectively secured in non-rotatable clevises 88 to prevent relative rotation between the ram and the cylinder as the ram is moved.

In this embodiment of the invention, the ram 86 is provided with a series of external, circumferential grooves which, in the illustrated construction, are formed by a helical groove 93 having a relatively small helical angle as compared to the groove 32 shown in FIG. 1. Adapted to lockingly engage the ram 83 are a pair of opposed, arcuate pawls 94 and 95 which are milled or otherwise shaped on their inner surfaces to form oppositely sloping helical teeth 96 and 97, respectively. The helical angle of the teeth 96 and 97 corresponds to that of the groove 93 so that the teethmay be interfitted in the groove when the pawls are moved radially inwardly toward the ram 83-. As shown, the pawl assemblies are carried in the upper cylinder head 81 so that they are accessible for replacement. It will be apparent that, in this alternate embodiment of the invention, the ram 83 can be provided with a series of circular grooves along substantially its entire length instead of the continuous helical groove 93. In such an instancethe pawl teeth 96 and 7 would be correspondingly modified to interfit within the circular grooves.

Referring particularly to the pawl 9'4, it will be seen that each helical pawl tooth 96 is formed to slope downwardly to a horizontal shoulder 93 at the bottom of the tooth. This tooth formation prevents extension of the ram when the tooth is interfitted in the groove S 3, while being capable of ratcheting to permit opposite or downward ram movement. The pawl 94 is normally urged into locking engagement with the ram by the compression springs 99 which act between an outer annular surface of the pawl and an adjacent inner annular surface of the cylinder head 81. Reverse or disengaging movement of the pawl is affected by movement of a piston 100 that is similar to the pawl 45. This piston is reciprocally mounted in an open-ended bore 191, which is cut through the side of the head member 81 and closed 'at its outer end by the plate 102, the piston being connected to the pawl 94 by a bolt 103'. The shank of the bolt 103 loosely extends through the pawl 94 into threaded engagement with the piston, while the head of the bolt is seated in a recess in the inner surface of the pawl.

Fluid may be introduced into the bore 101 behind the head of the piston 190 through a passage 108 and a conduit 169 which connects to the cylinder head 81 in fluid communication with the passage. It will thus .be seen that, when the fluid pressure admitted to the bore 101 exceeds the biasing force of the springs 99, the pawl 94 will be pulled out of engagement with the ram. As shown most clearly in FIG. 7, the pawl 94 is relieved at its inner end surfaces in the areas, generally designated by reference numeral 110, so that only a relatively small amount of movement is required to disengage the pawl.

The locking action of the pawl 94 is made responsive to the fluid pressure in the cylinder 80 by connecting the lower end of the conduit 109 to the lower cylinder head 82. in fluid communication with the passage 1.11. As previously described in connection with the preferred embodiment of the invention, the force exerted by the pawl springs 99 and the relative areas of the head of the piston and the piston 84 are such that the pawl 94 will be disengaged by fluid pressure before it can be damaged by movement of the ram 83. However, in the event the load on the ram changes to tension after it is partially extended, the pressure in the cylinder will drop and the spring 99 will force the pawl to again engage the ram to prevent further undesirable extension.

The construction of the pawl 95 is generally the same as that of the pawl 94 except that each pawl tooth 97 slopes downwardly from an upper horizontal shoulder 115. By reason of this configuration, engagement of the tooth 97 in the ram groove 93 will prevent downward ram movement, while permitting the ram to ratchet upwardly.

Compression springs 116, acting between the pawl 95 and the inner surface of the cylinder head 81, urge the pawl into normal engagement with the ram to prevent retraction thereof. The inner end surfaces of the pawl are relieved in the areas 120 (FIG. 7) so as to reduce the amplitude of outward movement of the pawl for disengaging it from the ram to permit it to retract. In the illustrated construction, the corner of one end of a lever arm 117 is pivotally connected to a pin 118 which slidably extends through the cylinder head 81 into fixed engagement with the pawl 95. The opposite corner of the same end of the lever arm is pivotally connected at 119 to the cylinder head. Thus, downward movement of the free end of the lever arm 1'17 serves to pull the pin 118 and pawl 95 out of engagement with the ram. When the ram 83 is loaded with a compression load, it is usually necessary to slightly raise the ram by increase of fluid pressure in the cylinder 80 before the lever arm 117 can be swung to disengage the pawl.

The operation of the apparatus shown in FIGS. 6 and 7 is essentially the same as disclosed in connection with the preferred embodiment shown in FIGS. 1-5. In summary, the initial build-up of fluid pressure in the cylinder 80 effects a corresponding increase in pressure behind the piston 100 and causes the piston to move, thus disengaging the pawl 94 from the ram. As the pressure in the cylinder is increased the ram 83 is moved in ratcheting engagement with the pawl 95 to a selected position of extension, at which time the pressure source is cut-off. When the lever 117 is swung to disengage the pawl 95 from the ram to permit it to retract, the ram moves in ratcheting engagement with the pawl 94 during the retraction.

The pawl 95 serves as a safety means which prevents retraction of the ram until disengaged by movement of the cam arm 117. Extension of the ram beyond the selected position is prevented by the pawl 94 which will be forced into engagement with the ram should there' be a pressure drop below the ram piston 84.

The illustrated pawl construction of this modified embodiment of the invention may obviously comprise four quadrantal pawls arranged around the ram 83 instead of only the two, substantially semi-circular pawls 94 and 95 illustrated and described above. In such an instance, two diametrically opposed pawls are constructed and operated the same as the pawl 94, while the other two diametrically opposed pawls correspond to the pawl 95.

The advantage of this latter construction is that heavy tension or compression loads on the ram will be resisted on two opposed side areas of the ram instead of on only one side, thus reducing eccentricforces which might tend to bend the ram and cause binding at the surfaces of sliding engagement of the ram with the cylinder head 81 and of the piston 84 with the cylinder 80. However, it will be apparent that the operation of the locking mechanism remains unchanged.

The foregoing indicates the versatility of the principles of the locking mechanisms of the invention. Obviously,

many other modifications and variations of the disclosed embodiments of the invention will be apparent to those skilled in the art in light of the above teachings. It is to be understood therefore, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically disclosed.

What is claimed is:

l. A fluid actuator for producing relative movement between two members comprising a cylinder adapted to be connected to one of said members, a ram adapted to be connected to the other of said members and having one end connected to a piston axially slidable in said cylinder, said mam having a helical groove extending substantially its entire length, a nut, means rotatably mounting said nut said cylinder with said ram extending axially therethrough, said nut having a tooth on its inner surface engaged within said groove for rotating the nut in response to axial movement of said ram, said nut having a peripheral array of radially extending teeth, pawl means normally engaging said radially extending teeth to lock said nut against rotation and the ram against movement in at least one direction, said pawl means being mounted on said cylinder for reciprocation toward and away from said nut, spring means urging said pawl means radially,

inwardly into normal nut-locking engagement with said radially extending teeth, and means operatively inter connected between said pawl means and said cylinder for moving said pawl means radially outwardly out of engagement with said radially extending nut teeth to permit said movement of said 2. A fluid actuator for producing relative movement between two members comprising a cylinder adapted to be connected to one of said members, a ram adapted to be connected to the other of said members and having one end connected to a piston axially slidable in said cylinder, means for applying fluid pressure between one end of said cylinder and said piston to move said ram,

said ram having a helical groove extending substantially its entire length, a nut, means rotatably mounting said nut within said cylinder with said ram extending axially therethrough, said nut having a tooth on its inner surface engaged with said groove for rotating said nut in response to axial movement of said ram, said nut having a peripheral array of radially extending teeth, a one-way pawl mounted on said cylinder for radial reciprocation toward and away horn said nut, spring biasing means urging said operatively interconnected between said cylinder and pawl for moving it radially outwardly out of engagement with said radially extending nut teeth to permit movement *of said ram in said one direction.

3. A fluid actuator for producing relative movement between two members comprising a cylinder adapted to be connected to one of said members, a ram adapted to be connected to the other of said members and having one end connected to a piston axially slidable in said cylinder, said ram having a helical groove extending substantially its entire length, a nut, means rotatably mounting said nut within said cylinder with said ram extending axially thereth-rough, said nut having a tooth on its inner surface engaged within said groove for rotating the nut in response to axial movement of said ram, said nut having a peripheral array of radially extending teeth, a first one-way pawl normally engaging said radially extending teeth to lock the nut against rotation and the ram against movement in one direction, said pawl being mounted on said cylinder for reciprocation toward and away from said nut, spring biasing means urging said pawl radially inwardly into normal nut-locking engagement wit-h said radially extending teeth, means for applying fluid pres sure to said pawl to move it radially outwardly out of engagement with said radially extending nut teeth, and means for applying pressure to said cylinder to move said ram in said one direction.

4. The actuator claimed in claim 3 wherein said first fluid pressure means comprises a conduit connected to said cylinder whereby fluid actuation of said first pawl is responsive to fluid pressure in said cylinder tending to move said ram in said one direction.

5. The actuator claimed in claim 3 including a second one-way pawl for locking said ram against movement in direction opposite to said one direction, means mounting said second pawl on said cylinder for radial reciprocation, spring means carried by said latter-mentioned mounting means and acting on said second pawl to move it radially inwardly into locking engagement between said radial-1y extending nut teeth, and means connected to said second pawl for moving it outwardly to disengage said radially extending nut teeth and permit movement of said ram in said opposite direction.

6. The actuator claimed in claim 3 wherein said means rot-atably mounting said nut comprises a pair of axially spaced plates connected to said cylinder, said nut being disposed between said plates, and a pair of spring washers between the upper and lower surfaces of said nut and said axially spaced plates, said spring washers acting to normally rotatably suspend said nut out of frictional contact with said plates and being individually collapsible against the adjacent plate when said nut is locked against rotation by said pawls and a load is applied axially to said actuator in either direction.

7. A fluid actuator for producing relative movement between two members comprising a cylinder adapted to be connected to one of said members, a ram adapted to be connected to the other of said members and being connected to a piston axially slidable in said cylinder, said ram having a helical groove extending substantially its entire length, a first one-way pawl, means mounting said first pawl on said cylinder for radial reciprocation, a helical tooth on the radially inner surface of said pawl for interfittingly engaging within said groove to lock said ram against movement in one direction, spring means carried by said actuator and acting on said pawl to move it radially inwardly into a position of normal locking engagement, first fluid pressure means connected to said actuator for applying fluid pressure to said first pawl to move it radially outwardly from said position of locking engagement, and second fluid pressure means connected to said cylinder for applying fluid pressure to move said ram in said one direction.

8. The fluid actuator claimed in claim 7 including a second one-way pawl, means mounting said second pawl on said cylinder for radial reciprocation, a helical tooth on the radially inner surface of said second pawl for lockingly interfitting in said groove to lock said ram against movement in a direction opposite to said first direction, spring means carried by said actuator and acting on said second pawl to move it radially inwardly into a position of locking engagement, and manually-actuatable release means connected to said second pawl for moving it radially outwardly to unlock said ram for movement in said opposite direction.

9. The actuator claimed in claim 7 wherein said first fluid pressure means comprises a conduit connected to said cylinder whereby fluid actuation of said first pawl is responsive to fluid pressure in said cylinder tending to move said ram in said one direction.

10. In a fluid actuator including a cylinder and a ram having a piston on one end axially slidable in said cylinder, the improvement comprising a first one-way ramlocking means mounted on said actuator, said first locking means normally being in a condition of operative engagement with said ram to lock it against movement in one direction and being actuatable by fluid pressure to an unlocked condition of operative disengagement with said ram, means connected to said actuator in fluid communication with said cylinder and said first locking means and operable for applying fluid pressure to said piston to effect movement of said ram in said one direction and to said first locking means for moving the same to said second condition in which said ram is unlocked for movement in said one direction, and a second ram locking means carried by said actuator for normally locking said ram against movement in a direction opposite to said one direction, said second locking means being releasable to unlock said ram for movement opposite to said one direction.

11. The actuator claimed in claim 10 including means responsive to relief of the fluid pressure to said first locking means for urging the first locking means to its normal locking condition.

12. The fluid actuator claimed in claim 10, including means for automatically relieving the fluid pressure applied to hold said first locking means in said unlocked condition in response to a drop in fluid pressure applied to said piston.

13. The actuator claimed in claim 10, including manually actuatable releasing means carried by said actuator and connected to said first ram-locking means for actuating it to said unlocked condition.

14. A fluid actuator for producing relative movement i etween two members comprising a cylinder operatively connected to one of said members, a ram having one end connected to the other of said members and its opposite end connected to a piston axially slidable in said cylinder, said ram having external groove means extending sub stantially its entire length, fluid pressure-actuatable first ram-locking means mounted on said cylinder, said first ram-locking means normally being in a condition of locking engagement with said groove means to prevent movement of said ram relative 'to said cylinder in one direction, first fluid pressure means connected to said actuator in fluid communication with said locking means for actuating it to an unlocked condition, second fluid pressure means connected to said actuator in fluid communication with said cylinder for affecting movement of said ram in said one direction, and a releasable second ram locking means caried by said cylinder, said second ramlocking means being in normal locking engagement with said groove means to prevent movement of said ram opposite to said one direction and comprising manually operable means for releasing the same.

15. The actuator claimed in claim 14 wherein said firs-t and second fluid pressure means are balanced in fluid circuit relation to actuate the first ram-locking means H- to its unlocked condition when fluid pressure is applied to said cylinder for moving the ram in said one direction.

16. The actuator claimed in claim 15, including spring biasing means carried by said actuator and acting on said first locking means to urge the same into said position of normal locking engagement with said groove means for automatically locking the ram against movement in said one direction when the fluid pressure in said cylinder is relieved.

17. The actuator claimed in claim 16, including means connected to said first ram-locking means for manually releasing the same from locking engagement with said groove means.

18. A fluid actuator for producing relative movement between two members comprising a cylinder adapted to be connected to one of said members, a ram adapted to be connected to the other of said members and having one end connected to a piston axially slidable in said cylinder, said ram having a helical groove extending substantially its entire length, fluid pressure-releasable first ram-locking means carried by said actuator for normally locking said ram against movement in one direction, said fluid pressure-releasable first ram-locking means including a first one-way pawl, means mounting said first pawl on said cylinder for radial reciprocation, spring biasing means carried by said pawl mounting means for urging said first pawl toward said ram into a position of normal operative locking engagement with said groove,

first fluid pressure means connected to said pawl mounting means for applying fluid pressure to said first pawl to move it away from said ram into a second unlocked position of operative disengagement from said groove, and second fluid pressure means connected to said cylinder for applying fluid pressure to said piston to cause said acting on said second pawl for moving it into normal locking engagement with said groove, and means connected to said second pawl for moving it away from said ram in opposition to said yieldable means.

19. The fluid actuator claimed in claim 18 wherein said first and second fluid pressure means are connected in balanced fluid circuit relation to apply actuating fluid pressure to said first pawl in response to the fluid pres sure applied to actuate said piston.

References Cited in the file of this patent UNITED STATES PATENTS I 2,349,244 Brown May 23, 1944 2,698,157 Ludeman Dec. 28, 1954 2,804,054 Geyer Aug. 27, 1957 

10. IN A FLUID ACTUATOR INCLUDING A CYLINDER AND A RAM HAVING A PISTON ON ONE END AXIALLY SLIDABLE IN SAID CYLINDER, THE IMPROVEMENT COMPRISING A FIRST ONE-WAY RAMLOCKING MEANS MOUNTED ON SAID ACTUATOR, SAID FIRST LOCKING MEANS NORMALLY BEING IN A CONDITION OF OPERATIVE ENGAGEMENT WITH SAID RAM TO LOCK IT AGAINST MOVEMENT IN ONE DIRECTION AND BEING ACTUATABLE BY FLUID PRESSURE TO AN UNLOCKED CONDITION OF OPERATIVE DISENGAGEMENT WITH SAID RAM, MEANS CONNECTED TO SAID ACTUATOR IN FLUID COMMUNICATION WITH SAID CYLINDER AND SAID FIRST LOCKING MEANS AND OPERABLE FOR APPLYING FLUID PRESSURE TO SAID PISTON TO EFFECT MOVEMENT OF SAID RAM IN SAID ONE DIRECTION AND TO SAID FIRST LOCKING MEANS FOR MOVING THE SAME TO SAID SECOND CONDITION IN WHICH SAID RAM IS UNLOCKED FOR MOVEMENT IN SAID ONE DIRECTION, AND A SECOND RAM LOCKING MEANS CARRIED BY SAID ACTUATOR FOR NORMALLY LOCKING SAID RAM AGAINST MOVEMENT IN A DIRECTION OPPOSITE TO SAID ONE DIRECTION, SAID SECOND LOCKING MEANS BEING RELEASABLE TO UNLOCK SAID RAM FOR MOVEMENT OPPOSITE TO SAID ONE DIRECTION. 